Certain eye conditions can be treated with ocular lenses which adjust the optical properties of the eye. Such lenses include contact lenses, artificial corneas and intraocular lenses.
In the example of intraocular lenses, the normal crystalline lens of an eye is replaced with an intraocular lens formed of materials such as polymethyl methacrylate, virgin silicone or acrylic based materials, which are generally soft and flexible to allow the lens to be folded for insertion via a small incision in the eye.
Patients fitted with ocular lenses often report visual disturbances including glare, streaks and/or shadows in the temporal visual field. These visual disturbances are termed photic disturbances. In the pseudophakic human eye in particular (where the crystalline lens has been surgically removed and replaced) photic disturbances (in this case termed pseudophakic dysphotopsia) can adversely affect the quality of vision of a high proportion of patients implanted with an intraocular lens.
Where secondary images are formed in the temporal visual field, the photic disturbances are termed positive dysphotopsia. Where shadows are formed in the temporal visual field, the photic disturbances are termed negative dysphotopsia. In pseudophakic patients the temporal field of vision can be constricted.
It has been shown that reflected rays of oblique light can cause phototic disturbances, as outlined in U.S. Pat. No. 7,217,289, the disclosure of which is incorporated herein by reference.
Such photic disturbances are common as greater than 50% of light striking the anterior eye is scattered, with a portion of the reflected light falling incident on the eye at oblique angles. Furthermore, the lens of the eye (natural crystalline or intraocular lens) is subject to peripheral light focusing over a broad range of angles, for example, up to 30°. The reason that positive dysphotopsia is noticeable is that the arcs of light that are focused on the nasal retina are 3.7 to 4.8 times more intense than incident light and so are perceived as brighter than the background illumination.
Negative dysphotopsia (temporal darkness) occurs when light is shunted away from the peripheral retina by the prismatic effect of many modern intraocular lenses. This phenomenon can also result in a reduction of the peripheral field in the order of 20%, reduces quality of vision, and hinders the ability of ophthalmologists to clinically view the peripheral retina by ophthalmoscopy.
The present invention seeks to provide an improved design for ocular and intraocular lenses which is believed to alleviate or eliminate photic disturbances, improve field of vision and/or visualisation of the peripheral retina. The present invention further seeks to improve the ability of ophthalmologists to clinically view the peripheral retina by ophthalmoscopy.
The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.